Effect of environment on the scale formed on oxide dispersion strengthened FeCrAl at 1050°C and 1100°C

Unocic, Kinga A.; Essuman, E.; Dryepondt, Sébastien; Pint, Bruce A.

doi:10.3184/096034012x13317275660176

Cited by 39 publications

(11 citation statements)

References 24 publications

(14 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Figures 1b and 1c show maps from a region at the metal-scale interface where Hf, but not Ti, was found to segregate to an adjacent grain boundary. It was recently discovered that Ti can be depleted in FeCrAl adjacent to the scale and not segregated to the adjacent grain boundaries [24]. This same behaviour was observed in X4 þ La with Ti found segregated to the alumina grain boundaries closer to the gas interface [23].…”

Section: Methodsmentioning

confidence: 81%

“…The rapid outward transport of Ti may explain the lack of Ti segregation if Ti becomes depleted in the substrate. Some indication of this has been found on yttria-dispersed FeCrAl [24].…”

mentioning

confidence: 90%

“…The initial observation of segregation of only Hf to the bare X4 þ La superalloy was resolved by the later observation that Ti segregation is more likely near the gas interface of the alumina scale and can be absent near the metal interface (as in Figure 1) due to Ti depletion in the adjacent metal. This difference has been observed in both FeCrAl and X4 þ La [23,24]. The smaller Ti ion (0.61 Å ) is known to diffuse rapidly through scales, forming Ti-rich oxides at the gas interface [2,4,18,19].…”

mentioning

confidence: 97%

See 2 more Smart Citations

Ionic segregation on grain boundaries in thermally grown alumina scales

Pint

Unocic

2012

Materials at High Temperatures

View full text Add to dashboard Cite

This study first examined segregation behaviour in the alumina scale formed after 100 h at 1100 C on bare and MCrAlYHfSi-coated single-crystal superalloys with~10 ppma La and Y. For the bare superalloy, Hf and Ti were detected on the grain boundaries of the inner columnar alumina layer. Increasing the oxidation temperature to 1200 C for 2 h did not change the segregation behaviour. With the bond coating, both Y and Hf were segregated to the grain boundaries as expected. However, there was evidence of Ti-rich oxide particles near the gas interface suggesting that Ti diffused from the superalloy through the coating. To further understand these segregation observations with multiple dopants, other alumina-forming systems were examined. Alumina scale grain boundary co-segregation of Ti with Y is common for FeCrAl alloys. Co-segregation of Hf and Ti was observed in the scale formed on co-doped NiAl. No La segregation was detected in the scale formed on NiCrAl with only a 19 ppma La addition, however, the scale was adherent.

show abstract

Section: Methodsmentioning

confidence: 81%

“…The rapid outward transport of Ti may explain the lack of Ti segregation if Ti becomes depleted in the substrate. Some indication of this has been found on yttria-dispersed FeCrAl [24].…”

mentioning

confidence: 90%

mentioning

confidence: 97%

See 1 more Smart Citation

Ionic segregation on grain boundaries in thermally grown alumina scales

Pint

Unocic

2012

Materials at High Temperatures

View full text Add to dashboard Cite

show abstract

“…Water vapor also could affect the transport through the alumina scale. Recent work studying the isothermal alumina scale growth rate in the presence of water vapor has shown that water vapor reduces the scale thickness at 1100°-1200°C [57,58]. However, these studies were conducted on FeCrAl-type alloys that do not form base-metal oxide layers like NiCrAl or NiPtAl compositions.…”

Section: Hvof/aps Coatings At 1100°cmentioning

confidence: 99%

The Effect of Water Vapor and Superalloy Composition on Thermal Barrier Coating Lifetime

Pint¹,

Haynes²,

Unocic³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

View full text Add to dashboard Cite

New power generation concepts may contain higher water vapor in the turbine combustion gas due to the fuel or to steam dilution. To assess the effect of higher water vapor content on thermal barrier coating performance, furnace cycle (1h) testing was conducted in air with 10, 50 and 90 vol.% water vapor and compared to prior results in dry O 2. The first series of experiments examined Pt diffusion (γ+γ') and Pt-modified aluminide (β) bond coatings on second-generation superalloy N5 at 1150°C with commercially vapor-deposited yttria-stabilized zirconia (YSZ) top coats. Compared to dry O 2 , the average coating lifetimes with Pt diffusion coatings were unaffected by the addition of water vapor while the Pt-modified aluminide coating average lifetime was reduced by >50% with 10% water vapor, but less reduction was observed with higher water contents. A similar set of coatings on low Re superalloy N515 showed no debit in lifetime with Pt aluminide bond coatings exposed to 10% water vapor. Characterization of the alumina scale thickness at failure showed a thicker oxide beneath the YSZ coating (compared to the scale without a top coating) for both types of bond coatings, and an increase in the oxide thickness with the addition of 10% water vapor. These observations were further studied using analytical transmission electron microscopy. The second series of experiments examined high velocity oxygen fuel (HVOF) MCrAlY and MCrAlYHfSi bond coatings and air-plasma sprayed YSZ top coatings on X4 superalloy substrates with and without Y and La additions. Compared to a dry O 2 baseline, the addition of 10% water vapor decreased the YSZ coating lifetime for either bond coating by ~30% at 1100°C. Substrates with Y and La additions showed no change in the average lifetime in 10% water vapor compared to standard X4. A further increase to 50% water vapor did not further decrease the average lifetime of one group of coatings. To better simulate base-load power generation, one group of specimens was cycled with 100h cycles, which substantially increased the coating lifetime. In each case, higher average lifetimes were observed with Hf in the bond coating. Initial characterization of the alumina scales formed at failure showed little effect of the water vapor addition, bond coating composition or substrate composition. For both series of coatings, the addition of 10% water vapor to the experiment reduced YSZ coating lifetime. However, increasing to 50% or 90% H 2 O showed no additional decrease in average YSZ lifetime.

show abstract

“…Oxidation of Metals (2020) 93:229-245 beneficial, in particular, at lower temperatures as it accelerates protective alumina scale growth [16][17][18][19][20][21][22][23][24]. 3.…”

mentioning

confidence: 99%

Reactive Element Effects in High-Temperature Alloys Disentangled

2019

View full text Add to dashboard Cite

Reactive elements-REs-are decisive for the longevity of high-temperature alloys. This work joins several previous efforts to disentangle various RE effects in order to explain apparently contradicting experimental observations in alumina forming alloys. At 800-1000 °C, "messy" aluminum oxy-hydroxy-hydride transients initially formed due to oxidation by H 2 O which in turn undergo secondary oxidation by O 2. The formation of the transient oxide becomes supported by dispersed RE oxide particles acting as water equivalents. At higher temperatures, electron conductivity in impurity states owing to oxygen vacancies in grain boundaries (GBs) becomes increasingly relevant. These channels are subsequently closed by REs pinning the said vacancies. The universality of the emerging understanding is supported by a comparative first-principles study by means of density functional theory addressing RE(III): Sc 2 O 3 , Y 2 O 3 , and La 2 O 3 , and RE(IV): TiO 2 , ZrO 2 , and HfO 2, that upon reaction with water, co-decorate a generic GB model by hydroxide and RE ions. At 100% RE coverage, the GB model becomes relevant at both temperature regimes. Based on reaction enthalpy ΔH r considerations, "messy" aluminum oxy-hydroxyhydride transients are accessed in both classes. Larger variations in ΔH r are found for RE(III)-decorated alumina GBs as compared to RE(IV). For RE(III), correlation with GB width is found, increasing with increased ionic radius. Similarly, upon varying RE(IV), minor changes in stability correlate with minor structural variations. GB decorations by Ce(III) and Ce(IV) further consolidate the emerging understanding. The findings are used to discuss experimental observations that include impact of co-doping by RE(III) and RE(IV).

show abstract

Effect of environment on the scale formed on oxide dispersion strengthened FeCrAl at 1050°C and 1100°C

Cited by 39 publications

References 24 publications

Ionic segregation on grain boundaries in thermally grown alumina scales

Ionic segregation on grain boundaries in thermally grown alumina scales

The Effect of Water Vapor and Superalloy Composition on Thermal Barrier Coating Lifetime

Reactive Element Effects in High-Temperature Alloys Disentangled

Contact Info

Product

Resources

About